The ex-Westlife singer and former husband of Kerry Katona has said he will fight "tooth and nail" in the coming months to get full custody of Molly, eight, and Lilly-Sue, seven.

Sources close to McFadden, 30, say it is "last-chance saloon" for the singer to win his children back and that he is willing to do anything it takes -- including a return to Ireland. He is now engaged to singer Delta Goodrem, 25, and lives in Australia.

McFadden was reported to have flown to the UK this weekend to have a showdown with his ex-wife.

The Sunday Independent can reveal: McFadden is planning to produce phone records in court to prove his attempts to contact his children.

He will tell the judge he has only managed to speak with his children three times since Christmas, despite weekly attempts on his behalf.

His partner, Goodrem, is fully supporting him in his plight and has told him to do "everything necessary" including moving back to Ireland for six months if it will help get his children back.

McFadden will give evidence on how Katona's actions have had serious health repercussions on a close family member who had to be hospitalised with stress.

The singer's claims are in stark contrast to an interview Katona gave in a British newspaper last week. She stated that McFadden rarely calls his children and that their youngest daughter Lilly "doesn't really know who he is".

Since reading the comments McFadden has told friends it is all-out war and that the time has come to get his children back.

"He is going to go all the way to get the children back now. He wanted to launch another custody battle before Christmas but his lawyers told him to be patient and wait a few months because it was too soon since he was last refused full custody," said a source.

"Now the time has come and Brian is going to give it everything he has got. He is meeting with lawyers and has built up a store of hard evidence to argue that the children would be better off living with him."

The source added that McFadden has a good, albeit long-distance, relationship with his daughters and is doing his best against the odds.

"Both of the children are always thrilled when they get to speak to him. They call him 'daddy' and tell him they love him but it upset Brian a lot when the kids got confused because Katona told them to call Mark [Croft, her former boyfriend] 'daddy' too. And now that relationship is over, the children are completely confused."

The source added: "His youngest little girl Lilly-Sue knows who he is. To suggest otherwise is ludicrous. He just has a somewhat stronger relationship with his eldest daughter Molly.

"She was a little older when the marriage broke down and he went to live in Australia, so she understands the situation a lot better and realises that it isn't Brian's fault."

Claims that McFadden only speaks to his daughters five times a year have "cut him to the core".

As the source explained: "He calls them twice a week; every week. But for reasons that will come out in court it is proving difficult to even talk to his children. He adores the girls and it's tearing him up to know he can't pick up the phone whenever he wants to.

"They're living with a cocaine-using mother. He is pulling his hair out, having sleepless nights wondering whether they're okay or being looked after and he will not stand for being labelled a bad dad."

McFadden is now adamant he will have his daughters by the end of the year.

"Since pictures were released of Kerry snorting cocaine in the bathroom of her own home and she has admitted to three-day coke binges while they are in the house, he is 100 per cent confident that the judge will rule in his favour this time around."

Molly and Lilly-Sue stayed with Katona after her split from McFadden in 2004.

Following Katona's interview McFadden posted a message on his Twitter site calling his ex-wife a "pig-faced mole" saying: "Wish certain f**ks would stop selling there [sic] stories to rags and get a real job. Kerry Katona you are dead to me!"

McFadden's angst-ridden tweets were later deleted and he admitted he "just lost it".

"I spoke from the heart," he said. "I might have been a bit over the top, but I was angry. I got my point across and I got to vent."